Orthopantomography, Scannography, Linear Tomography and Cephalography are complementary radiographic techniques, often combined in a single equipment, of widespread use in dental radiology to obtain respectively a comprehensive survey of the maxillo-facial complex, tomographic views of selected anatomical districts under transversal or axial projections, and cranial views under multiple projections, supporting the diagnosis in the dental prevention, restoration and follow up.
Orthopantomography aims to produce a radiographic image of a curved plane approximating the patient jaws, with blurring of the anatomical structures laying outside a narrow layer around the predesignated curved plane, by using the relative movement of the radiographic film versus the rotation of the x-ray source to generate the layer forming effect.
Scannography has a layer forming process similar to Orthopantomography, where the object is typically laying on a flat plane. It is practically used to produce axial or transverse views of specific anatomical districts, such as the jaw, the joints and the sinus.
Linear Tomography is an alternative technique, using the classic linear tomographic layer forming projection. It is practically used to produce axial or transverse views of specific anatomical districts in the jaw.
Cephalography is a stationary radiographic technique, aiming to produce radiographic images of the cranial complex under various projections, with minimum magnification and geometrical distortion.
For all radiographic modalities the real-time digital x-ray image acquisition is nowadays a more and more interesting option, allowing removal of the film processing and related chemicals, by taking advantage of the improved performances and reduced costs provided by the modem image sensor technology.
Prior art (U.S. Pat. No. 4,188,537) describes apparatus and methods in which Real-time Digital Panoramic Radiography is implemented by an array of multiple detectors, or a vertical scanning single detector, where vertical lines are acquired in synchronisation with the rotation movement, so generating and displaying a panoramic image. This solution is deficient, as it is lacking the layer forming effect.
Other prior art (U.S. Pat. No. 4,878,234) describes apparatus and methods in which Real-time Digital Panoramic Radiography is implemented by CCD image sensors where vertical lines in the image zone are clocked out in the not-illuminated storage zone, by a frequency simulating the speed of the moving x-ray film in the conventional Dental Panoramic Tomography.
In other prior art arrangements (U.S. Pat. No. 4,823,369) Real-time Digital Panoramic Radiography is implemented by x-ray image detectors, preferably consisting of amorphous silicon, where complete frames corresponding to the active area are acquired at sufficiently fast frequency and adjacent frames are added as a function of time, either by pre-processing in order to obtain the panoramic image on one selected layer, or by storing in memory and later processing, so giving the possibility of multiple layer reconstruction.
Further prior art arrangement (U.S. Pat. No. 4,995,062) describe apparatus and methods in which Real-time Digital Panoramic Radiography is implemented by CCD image sensors where different vertical lines are driven with different clock frequency so simultaneously obtaining a plurality of tomograms at different depths of the jaw.
Another prior art arrangement (U.S. Pat. No. 5,195,114) describe apparatus and methods in which Real-time Digital Panoramic Radiography is accomplished by an X-ray image detection system, typically based on a signal intensifier tube camera (SIT), where video signal is acquired and stored in a storage unit (such as video tape recorder), and frame digital data are lately derived by A/D conversion and processed selecting frame interval and shift depending on the movement speed of the target, to digitally form the panoramic image of given tomographic layers. This arrangement is limited in the video rate acquisition, and does not provide enough resolution for adequate panoramic image reconstruction. The process is also time consuming and, in case of digital frame storage, would require huge amount of memory.
More recent prior art arrangement (EP 0 673 623) describe apparatus and methods in which Real-time Digital Panoramic Radiography is implemented by X-ray detection system having an area coincident with the cross-section area of the X-ray and so requiring only one narrow slit X-ray diaphragm located on the X-ray source. By this arrangement the Panoramic image reconstruction is accomplished either by frame acquisition, with intermediate frame storage (memory consuming option) or with immediate frame processing (less memory consuming option), or by the TDI method: in the first case for adequate layer formation the frame resolution must be chosen in a way to ensure that each point of the final reconstructed image is represented in more positionally shifted images (preferably five or more); in the second case (even less memory consuming) the image is directly integrated and formed on the X-ray detector, by controlling the clock sequence in a way to ensure that the projected image of a point within the sharp layer of the object will be represented by the same spatial position in the final reconstructed panoramic image.
In Digital Panoramic Radiography, the following desirable features are applicable:    to be able to generate simultaneously a plurality of panoramic tomograms at different depths of the jaw.    to have an accurate, reproducible and inexpensive method of simulating the speed of the x-ray detector (the radiographic film). This information is necessary for the layer forming processing required in the tomosynthesis of the panoramic image.    In the case where full frame acquisition is used, to have a method to adapt to the varying dynamic of the exposure signal in a way to optimise the signal response of the detector in terms of signal to noise ratio.
Both in Real-time Digital Panoramic Radiography, Transversal Tomography and Cephalography it is another desirable feature to have a common electronic hardware capable of serving with efficient and fast response x-ray image sensors of various kind and structure and different scanning methods such as TDI or frame transfer.
The purpose of this invention is to advantageously offer technically efficient and economic solution to all the desirable features above.